Move the search to a dedicated search page

[tomodwyer]

Currently all searching for Codelists takes place on the home page. This limits our ability to modify the home page, and means that the home page "hero" section is shown on all search results page.

We should move the searching and search results page to a new URL (for example /search) and enable the form on the home page to take users to search results at that URL. We should redirect all old search URLs to the new search page, so any legacy links will continue to work.

This should also help in creating a much more performant home page (see #1640), and open a pathway to a redesign of the home page.